After 9 great years of making belt drive kits for the X2 community the time has come for a change. I am currently in the process of a hand off of the belt drive kit manufacturing to www.LittleMachineShop.com (LMS). They are preparing to start making these kits and will have them for sale within the next few months. These will be the same high quality kits that X2 users have buying from Steele Company, LLC (www.stirlingsteele.com). I hope that you can give your future belt drive business to LMS. They are a great resource for mini-mill and mini-lathe users and pretty much anyone who has or wants a little machine shop of their own.
No there really wouldn't be an advantage to having ball screws replace the standard lead screws on a manual X2. The ball screws provide much lower turning friction than acme type lead screws and for this reason they are desirable for stepper or servo motor driven axies.